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2 1. Introduction to SiC 1.1 History of SiC SiC is a compound composed of covalent and partial ionic bonds of silicon and carbon. In 1824, Jons Jakob Berzelius is credited with identifying chemical bonds between Si and C for the first time. After that, non-systematic synthesis methods were reported by Despretz (1849), Marsden(1880), Colson(1882), etc, and, and large-scale commercial production is credited to Edward G. Acheson. Edward G. Acheson devised a method for making SiC powder in 1891 (Acheson Process). After patenting the method in 1893, he established Carborundum to manufacture the material. In the past, the term Carborundum was used instead of SiC. While dissolving carbon in a corundum (alumina) solution, he discovered that blue-black crystals were synthesized, which he believed to be a compound of carbon and corumdum and named Carborundum. Carborundum was initially as an abrasive due to its Mohs hardness 9. Later, Ferdinand H. Moissan first discovered a trace of SiC powder found in the Canyon Diablo meteorite in Arizona, and showed that SiC naturally occurs in nature. After that, the mineral type SiC is called Moissanite in his honor. Currently, Moissanite is used as a trade name for SiC gemstones. Fig 1.1 Naturally occurring SiC crystal vs. artificially synthesized SiC crystal (Source : academic data) 5

3 2. SiC powder 2.1 SiC power manufacturing process The laboratory scale production of SiC was made about 150 years ago. Realizing the importance of abrasives and cutting materials, Acheson developed a process for making silicon carbide powder as a commercial solvent, which has been used to produce SiC until now. This material has the second highest hardness (Mohs hardness 9-10) to diamond. Although it is mainly used as an abrasive or cutting material, it is also used as a refractory brick. About 10,000 tons of SiC bricks, for instance, are used in steel plants each year, and some industries have more need of this material as an refractory material rather than an abrasive. The ceramic industry is showing growing interest in the application of SiC as a structural material due to its high density and high strength. In general industries, SiC is considered as one of the most promising materials to substitute metal used in ceramic engines and gas turbines. In the nuclear industry, it can be used as nuclear fuel cladding, a refractory brick, a ceramic filter for incinerators, and a plasma shielding material for fusion reactors. SiC for commercial use is attained by heating a mixture of silica and coke (carbon). The basic reaction can be expressed as follows. SiO2 + 3C(s) SiC(s) + 2CO(g) Since the formation of SiC is based on an exothermic reaction, the heat generated by the reaction is used for self heating without external heat supply. Only a few days after the reaction, a rainbow-colored black or green mixture can be attained. This mixture is pulverized and separated according to particle size. In general, it is hard to sinter particles of 10 μm or more. SiC powder used to manufacture refractory bricks is produced by mixing and heating coarse powder, silicon nitride as a binder, nitride-oxide, and aluminosilicate glass or through reaction sintering of silicon and carbon. SiC used as a heating element is combined by heating high purity powder at A small amount of SiC powder is attained by pyrolysis of gas prepared by mixing volatile silicon and carbon (CVD). 6

4 3. Sintered SiC SiC has many advantages such as high strength and hardness, excellent high temperature properties, radiation resistance and resistance against plasma corrosion. These excellent properties of SiC are due to a high level of covalent bonding of SiC (~88%). Due to the extremely low self diffusion coefficient caused by the covalent quality, however, it is hard to densify pure SiC through typical powder metallurgy without pretreatment such as mechanical alloying, it can be densified only when high temperature of more than 2100 and high pressure are applied at the same time. With the current trend toward narrower line-width and larger diameter wafers in the next-generation semi-conductor industry, preventing contamination of Si wafers caused by particles during the process is becoming an important issue, and there is growing needs for materials for high strength and high elastic modulus and conditions to meet high temperature processes. Despite the high manufacturing costs, there is increasing demand for SiC for semi-conductor applications because of its advantages in terms of thermal and mechanical properties, chemical stability, and particle contamination compared to quartz glass and alumina. Table 3.1 shows properties of conventional molten quartz glass and Table 3.1. Properties of High Purity SiC and Quartz Glass high purity sintered SiC, and reaction sintered SiC. (Source : academic data) 7

5 4. SiC single crystals 4.1 Characteristics of SiC single crystals SiC is an artificial compound composed of covalent and partially ionic bonds and has one 3C-SiC cubic polytype called β-sic, about 70 kinds of hexagonal polytypes, and about 170 kinds of rhombohedral polytypes. All polytypes but the cubic type are called α-sic. Among them, the most common types include 3C-SiC, 4H-SiC, and 6H-SiC, which are widely used for commercial use. Since each polytype has a different energy band gap and charge mobility, related research is conducted in various areas. Fig 4.1 Structures of SiC polytypes Fig 4.2 Crystal structures of Si and SiC Si SiC(4H-SiC) Diamond structure 4H polytype (Source : Silicon carbide single crystal growth methods and applications, ) 8

6 5. SiC single-crystal business trend As the paradigm shifts toward low carbon and green growth with increasingly strict environmental regulations, there are growing needs for power saving features. With increasingly serious energy depletion and global environmental problems, there is an urgent to need to switch toward green energy technologies by developing technologies that can save energy and resources. Since ultra high purity SiC has 3 times higher thermal conductivity and 10 times higher breakdown strength than silicon, it can be used to produce energy efficient semi-conductor that operate at high temperature and high voltage or parts that normally operate even at extremely high temperature of 500. Likewise, SiC semi-conductor devices are used for high output substrates and power semi-conductors due to the excellent properties. Especially, since SiC power semiconductors can consume only 1/100 of power consumed by existing silicon power devices, more extensive applications are expected. Fig 5.1 Value chain of SiC industry Raw material Key material Component Application Ultra high purity SiC powder SiC Wafer Energy semiconductors for high efficiency power conversion Power semiconductor applications: computers, EVs, home appliances, industrial electronics, communication SiC Wafer Yakushima H.C.Starck Saint Gobain Cree II-VI Nitride Crystal Nippon Steel STM Electronics NXP TI / Infineon Sanyo / Hitachi Maxim etc. Leading companies: majority of carmakers, and majority of electronic companies (Source :Ceramics Material Industry Analysis, ) 9

7 6. Business trend 6.1 Entire business trend In the SiC substrate market, Cree (US), is taking the lead, and about 10% of high power LEDs are using SiC substrates. Currently, Cree, Dow Corning (USA), Nippon Steel, and Bridgestone (Japan) are producing 2-4 inch wafers, and SiCrystal(Germany) and Norstel (Sweden) are producing 2-inch wafers and developing 4-6 inch wafers. In particular, Cree and Nippon Steel introduced 6-inch prototypes, and both companies signed a cross license agreement for the SiC singlecrystal wafer business on April, Thus, it is expected that 6-inch products of several makers will be massproduced and available in the market and can be adopted in existing manufacturing lines for power semi-conductors in Recently, Tankeblue (China) has developed and begun to massproduce 2-inch wafers, but is still considered to lag behind in terms of product quality. Fig 6.1 Major SiC single-crystal manufacturers TanKeBlue Norstel Sicrystal SKC(Crysband) Bridgestone Nippon Steel Sumitomo Materials Denso Ⅱ-Ⅵ Inc. Dow Corning Cree SiC systems (Source :SNE Research) 10